Update to v4.17.3 kernel headers.

Test: Builds, boots on a walleye.
Change-Id: I389d8b61ec00ea309e38d1b1a2e0dace48c21edb
diff --git a/libc/kernel/uapi/linux/elf.h b/libc/kernel/uapi/linux/elf.h
index bf35f6c..195ef09 100644
--- a/libc/kernel/uapi/linux/elf.h
+++ b/libc/kernel/uapi/linux/elf.h
@@ -331,6 +331,7 @@
 #define NT_PPC_TM_CTAR 0x10d
 #define NT_PPC_TM_CPPR 0x10e
 #define NT_PPC_TM_CDSCR 0x10f
+#define NT_PPC_PKEY 0x110
 #define NT_386_TLS 0x200
 #define NT_386_IOPERM 0x201
 #define NT_X86_XSTATE 0x202
@@ -354,9 +355,6 @@
 #define NT_ARM_HW_WATCH 0x403
 #define NT_ARM_SYSTEM_CALL 0x404
 #define NT_ARM_SVE 0x405
-#define NT_METAG_CBUF 0x500
-#define NT_METAG_RPIPE 0x501
-#define NT_METAG_TLS 0x502
 #define NT_ARC_V2 0x600
 typedef struct elf32_note {
   Elf32_Word n_namesz;